let step k st outs ins =
if st <> T.OO then k st outs ins else
match ins with
+ | "(decidability)" :: tl -> k T.OK ("(decidability)" :: outs) tl
| "(semigroup" :: "properties)" :: tl -> k T.OK ("properties)" :: "(semigroup" :: outs) tl
| _ -> k T.OO outs ins